It has been known that organic materials such as thermoplastic resin, thermosetting resin, natural or synthetic rubber, mineral oil, lubricating oil, adhesive, paint, etc. are deteriorated by an action such as heat, oxygen, etc. on production, processing and use to cause deterioration of the strength of the organic material due to a phenomenon (e.g. molecular cleavage, molecular closslinking, etc.), change in flow properties, coloring, deterioration of surface physical properties, etc., which results in decrease of a commercial value. It has hitherto been known that the organic material is stabilized by containing various phenol and phosphorous antioxidants for the purpose of solving these problems about heat deterioration and oxidization deterioration.
As the phosphorous antioxidant, a three-coordinate phosphorous compound such as tris(2,4-di-t-butylphenyl)phosphite is used.
However, these known phosphorous antioxidants had a problem that the stabilizing effect to heat deterioration and oxidization deterioration is insufficient.
On the other hand, as those for solving the problem of the phosphorous antioxidant, there is suggested, for example, a cyclic phosphite having a phenolic hydroxyl group, such as 2,10-dimethyl-4,8-di-t-butyl-6-{2-3-(3-t-butyl-4-hydroxy-5-methylphenyl)p ropionyloxy!ethoxy}-12H-dibenzod,g!1,3,2!dioxaphosphosine, etc. (JP-A-5-86084).
The present inventors have produced various phosphorous compounds and studied intensively in order to develop a phosphorous compound having improved stabilizing effect to heat deterioration and oxidization deterioration. As a result, it has been found that a specific cyclic five-coordinate phosphorous compound exhibits the excellent stabilizing effects. Thus, the present invention has been accomplished.